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B. Ananthanarayan

Publications and source records attributed to B. Ananthanarayan.

At least 127 records · Page 7Linked to original sources
arXiv2000

Renormalization Group Evolution and Infra-red Fixed Points in Minimal Supersymmetric Standard Model with Baryon and Lepton Number Violation

We study the renormalization group evolution and infra-red stable fixed points of the Yukawa couplings and the soft supersymmetry breaking trilinear couplings of the minimal supersymmetric standard model with baryon and lepton number (and R-parity) violation involving the heaviest generations. We show analytically that in the Yukawa sector there is only one infra-red stable fixed point. This corresponds to non-trivial fixed point for the top-, bottom-quark Yukawa couplings and the $B$ violating coupling $λ_{233}''$, and a trivial one for the $τ$-Yukawa coupling. All other possible fixed points are either unphysical or unstable in the infra-red region. We then carry out an analysis of the renormalization group equations for the soft supersymmetry breaking trilinear couplings, and determine the corresponding fixed points for these couplings. We also study the quasi-fixed point behaviour, both algebraically and with numerical solutions of the evolution equations, of the third generation Yukawa couplings and the baryon number violating coupling, and those of the soft supersymmetry breaking trilinear couplings. From the analysis of the fixed point behaviour, we obtain upper and lower bounds on the baryon number violating coupling $λ_{233}''$, as well as on the supersymmetry breaking trilinear couplings.

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arXiv2000

Infra-red fixed points in supersymmetry

Model independent constraints on supersymmetric models emerge when certain couplings are drawn towards their infra-red (quasi) fixed points in the course of their renormalization group evolution. The general principles are first reviewed and the conclusions for some recent studies of theories with R-parity and baryon and lepton number violations are summarized.

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arXiv1999

Effective Lagrangians in $2 + ε$ Dimensions

The failure of the the loop expansion and effective lagrangians in two dimensions, which traditionally hinges on a power counting argument is considered. We establish that the book keeping device for the loop expansion, a role played by (the reciprocal of) the pion-decay constant itself vanishes for $d=2$, thereby going beyond the power counting argument. We point the connection of our results to the distinct phases of the candidate for the effective lagrangians, the non-linear sigma model, in $d=2+ε$, and eventually for $d=2$. In light of our results, we recall some of the relavant features of the multi-flavor Schwinger and large $N_f$ $QCD_2$ as candidates for the underlying theory in $d=2$.

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arXiv1999

Infra-red stable fixed points of R-parity violating Yukawa couplings in supersymmetric models

We investigate the infra-red stable fixed points of the Yukawa couplings in the minimal version of the supersymmetric standard model with R-parity violation. Retaining only the R-parity violating couplings of higher generations, we analytically study the solutions of the renormalization group equations of these couplings together with the top- and b-quark Yukawa couplings. We show that only the B-violating coupling $λ^{''}_{233}$ approaches a non-trivial infra-red stable fixed point, whereas all other non-trivial fixed point solutions are either unphysical or unstable in the infra-red region. However, this fixed point solution predicts a top-quark Yukawa coupling which is incompatible with the top quark mass for any value of $\tanβ$.

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arXiv1999

Pion-Pion Scattering in Chiral Perturbation and Dispersion Relation Theories

Chiral perturbation theory, the low energy effective theory of the strong interactions for the light pseudoscalar degrees of freedom, is based on effective Lagrangian techniques and is an expansion in the powers of the external momenta and the powers of the quark masses, which correct the soft-pion theorems. Our primary emphasis will be on the problem of $ππ$ scattering. After briefly reviewing these features and some results, we review some features of $π-N$ scattering.

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arXiv1998

The Low Energy Expansion for Pion-Pion Scattering and Crossing Symmetry in Dispersion Relations

We show that a suitable setting for comparison of the low-energy representation for pion-pion scattering amplitudes, with dispersive representation for these amplitudes, is provided by certain manifestly crossing symmetric dispersion relations. We begin with a discussion of fixed-t dispersion relations and discuss the origin of crossing constraints that arise in this context when we consider resonance saturation with certain $l\geq 2$ states. We demonstrate that the approach advocated here does not require us to enforce such constraints. Our results are contrasted with those from fixed-t dispersion relations. We finally discuss the numerical import of our results.

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arXiv1997

Chiral Perturbation Theory for Nuclear Physicists

Chiral perturbation theory is the low energy effective theory of the strong interactions for the light pseudoscalar degrees of freedom. This program is based on effective Lagrangian techniques and is an expansion in the powers of the momenta and the powers of the quark masses, which correct the soft-pion theorems. After briefly reviewing these features and some results, we address the implications of this program to $π-N$ scattering, the $π-N$ sigma term and some recent investigations of the implications of chiral symmetry to nucleon-nucleon forces. We finally look at the implications of chiral perturbation theory to hadron mass relations.

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arXiv1997

Lectures on Unification

In these lectures we review the motivation, principles of and (circumstantial) evidence for the program of unification of the fundamental forces. In an appendix, we review the group theory pertinent to the program.

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arXiv1997

Higher Threshold Parameters in pi pi Scattering

A family of threshold parameters which probe the stability of chiral predictions is considered. The relevant criteria for the choice of threshold parameters are discussed. Sum rules for these quantities are derived from dispersion relations and evaluated from effective range formulae. Good agreement with two-loop chiral estimates for many of these quantities is found and interesting discrepancies are discussed.

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arXiv1997

Status of Supersymmetric Grand Unified Theories

We begin with a brief discussion of the building blocks of supersymmetric grand unified theories. We recall some of the compelling theoretical reasons for viewing supersymmetric grand unification as an attractive avenue for physics beyond the standard model. This is followed by a discussion of some of the circumstantial evidence for these ideas.

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arXiv1996

Scattering Lengths and Medium and High Energy $ππ$ Scattering

Medium and high energy absorptive parts contribute to dispersive expressions for D- wave scattering lengths, $a^0_2$ and $a^2_2$. For the model employed by Basdevant, Frogatt and Peterson we find the D- wave driving term contributions to the D- wave scattering lengths are $1.8\cdot 10^{-4}$ to $a^0_2$ and $0.4\cdot 10^{-4}$ to $a^2_2$, roughly $10\%$ and $30\%$ of their respective central experimental values. Inequivalent sets of sum rules are used as a compelling test of the consistency of the model for which crossing symmetry is not guaranteed. Results for the F- wave scattering length $a^1_3$ are presented, completing the recent Roy equation analysis of \pipi scattering in the range for $a^0_0$ favored by standard chiral perturbation theory.

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arXiv1996

The Non-Minimal Supersymmetric Standard Model at Large $\tanβ$

We present a comprehensive analysis of the Non-Minimal Supersymmetric Standard Model (NMSSM) for large values of $\tanβ$, the ratio of the vacuum expectation values of the two Higgs doublets, which arise when we impose the constraint of the unification of Yukawa couplings in the model. In this limit we show that the vacuum expectation value of the singlet is forced to be large, of the order of $10$ TeV. The singlet decouples from the lightest CP-even neutral Higgs boson and the neutralinos. We compare our results with the corresponding particle spectrum of the Minimal Supersymmetric Standard Model in the same limit. With the exception of the lightest Higgs boson, the particle spectrum in the model turns out to be heavy. The Higgs boson mass, after the inclusion of radiative corrections, is found to be in the neighbourhood of $\sim 130$ GeV.

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arXiv1996

The Chiral Coupling Constants $\lb{1}$ and $\lb{2}$ from \pipi Phase Shifts

A Roy equation analysis of the available $ππ$ phase shift data is performed with the $I=0$ S- wave scattering length $a^0_0$ in the range predicted by the one-loop standard chiral perturbation theory. A suitable dispersive framework is developed to extract the chiral coupling constants \lb{1}, \lb{2} and yields \lb{1}$=-1.70\pm0.15$ and \lb{2}$\approx 5.0$. We remark on the implications of this determination to (combinations of) threshold parameter predictions of the three lowest partial waves.

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arXiv1995

Radiative Electroweak Breaking with Pseudogoldstone Higgs Doublets

We consider a realistic example of supersymmetric grand unification based on $SU(3)_c \times SU(3)_L \times SU(3)_R$ in which the electroweak (EW) higgs doublets are `light' as a consequence of the `pseudogoldstone' mechanism. We discuss radiative EW breaking in this model, exploring in particular the `small' (order unity) and `large' $(\approx m_t/m_b)$ $\tan β$ regions by studying the variations of $r (\equiv \sqrt{μ^2_{1,2}/μ^2_3})$, where $μ^2_{1,2,3}$ are the well known MSSM parameters evaluated at the GUT scale. For $r$ sufficiently close to unity the quantity $\tan β$ can be of order unity, but the converse is not always true.

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arXiv1995

CP Violation in Heavy Neutrino Mediated $e^- e^- \to W^- W^-$

We consider the reaction $e^- e^- \rightarrow W^- W^-$ mediated by possible heavy neutrino exchange at future LINAC energies of $\sqrt{s}>> 2 m_W$. This reaction is sensitive to CP phases of the neutrino mixing matrices, even at the level of Born amplitudes. Certain integrated cross-sections are shown to have the power to resolve the CP phases when the experimental configurations are varied. Asymmetries sensitive to CP violation (involving initial QED phases) for $e^- e^-$ and $e^+ e^+$ reactions are constructed and their consequences considered.

hep-ph↗
arXiv1995

Particle Spectrum in the Non-Minimal Supersymmetric Standard Model with $\tanβ\simeq m_t/m_b$

We present a detailed discussion of the particle spectrum of the Non-Minimal Supersymmetric Standard Model (NMSSM), containing two Higgs doublets and a singlet, in the limit $\tanβ\simeq m_t/m_b$. This is compared with the corresponding particle spectrum of the Minimal Supersymmetric Standard Model (MSSM). In this limit the singlet vacuum expectation value is forced to be large, of the order of $10$ TeV, and the singlet decouples from the lightest scalar Higgs boson and the neutralinos. With the exception of the lightest Higgs boson, the particle spectrum in the model turns out to be heavy. The radiatively corrected lightest Higgs boson mass is in the neighbourhood of $\sim 130$ GeV.

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arXiv1995

Helicity-Flip Bremsstrahlung and the Measurement of CP-Violating Form Factors in Polarized $e^+e^-$ Collisions

Certain momentum correlations in the production and subsequent decay of heavy fermion pairs in $e^+e^-$ collisions have increased sensitivity to CP-violating electric and ``weak" dipole form factors of the fermion in the presence of longitudinal polarization of the $e^+e^-$ beams. However, unless the polarizations of $e^+$ and $e^-$ are equal and opposite, collinear initial-state radiation accompanied by helicity flip results in a CP-invariant contribution to these and acts as a background, and must be calculated and subtracted in order to isolate the CP-violating contribution due to the dipole form factor.We calculate this background contribution to such correlations, to order $α$, in $e^+e^-\rightarrow τ^+τ^-$ and $e^+e^-\rightarrow t\bar{t}$. For the anticitipated luminosities at $τ$-charm factories and SLC, for the $τ$, and at a future linear collider with centre-of-mass energy of 500 GeV for the top, these backgrounds are smaller than the statistical background and may be safely neglected.

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